The present invention relates to a process for producing conductors for integrated circuits using planar technology. It is applicable to the field of microelectronics and more specifically to the production of integrated circuits. It more specifically relates to conductors, which can be buried in a silicon oxide coating, e.g. carried by a magnetic garnet substrate for producing magnetic bubble stores.
The process of the invention essentially consists of making conductive deposits buried in an insulant covering a substrate, in such a way that these conductive deposits have no relief above the substrate surface. Thus, this process can be used in the production of planar integrated circuits.
A process for producing conductors for planar integrated circuits is already known and is for example described in the journal IEEE TRANSACTIONS AND ELECTRONIC DEVICES, vol. ED 2, no. 6, June 1980, article by B. M. WELCH entitled: "LSI processing technology for planar GaAs integrated circuits". This process is illustrated by the present FIG. 1. It essentially consists of depositing on a substrate 1 a coating of an insulating material 2 (e.g. silicon), followed by the deposition thereon of a masking coating 3 (e.g. of resin). This masking coating is then cut out down to the insulating material coating e.g. by irradiation through a mask. This cutting process makes it possible to obtain windows 4 in the masking coating and which correspond to the conductors to be obtained. This is followed by the etching of patterns in the insulating material coating 2 facing windows 4, e.g. by reactive ionization. This reactive ionization is well known and essentially consists of etching by ionization the insulating material coating, e.g. in a gaseous atmosphere. When the insulating material coating 2 has been etched, a conductive material 5 is then deposited on the masking coating and in the patterns etched in the insulating material coating 2. This is followed by the removal of the masking coating 3 and the conductive material covering the same, e.g. by dissolving the masking coating in a solvent (e.g. acetone) in the presence of ultrasonics. Masking coating lift-off is difficult if the conductive coating covering the same also covers the edges of the windows cut into the masking coating and reaches the insulating material coating 2. In order to successfully carry out lift-off of the masking coating by dissolving in a solvent, it is necessary for the edges of the masking coating to be vertical in the vicinity of the windows, which it is very difficult to ensure with conventional lithography means. If not and particularly when reactive ionic etching leads to a hardening of the masking coating surface, it is very difficult to dissolve this coating without the use of violent mechanical means, such as e.g. high pressure jets or brushing. The deposition of the conductive coating must be highly directional, so as not to cover the edges of the masking coating in the vicinity of the windows.
Another process for producing conductors for planar integrated circuits is known and is described in the journal IEEE TRANSACTIONS ON MAGNETICS, vol. MAG 16, no. 3, May 1980, article by Bernard J. ROMAN, entitled "Effect of conductor crossing on propagation". This process is illustrated by FIG. 2 and essentially consists of depositing an insulating material coating 2 on a substrate coating 1. This is followed by the deposition on said insulating material coating of a masking coating 3 (e.g. of resin), which is then cut by irradiation through a mask. This is followed by the etching of patterns in the insulating material coating 2, e.g. by reactive ionization, facing the windows 4 cut into the masking coating 3. This etching of the insulating material must be lateral, so as to bring about an increase in the dimensions of the patterns etched in the insulating coating compared with the dimension of the windows cut in the masking coating. This is followed by the deposition on said masking coating and on the bottom of the patterns etched in the insulating material coating 2 of a conductive material 5. This is followed by the removal of the masking coating and the conductive material covering the same by chemical etching of the masking coating.
The enlargement of the etched patterns in the insulating material coating by lateral etching leads to a poor definition of the dimensions of the conductors to be obtained. Moreover, an extra thickness of conductive material deposited in the etched patterns may lead to the formation of a junction between the coating of material to be deposited on the bottom of the patterns and the coating of material deposited on the masking coating. This junction will make it difficult to remove the masking coating by a solvent at the end of the process.